1. Field of the Invention
The present invention relates to a wood gasifier of the fixed bed type, and more particularly relates to an air supply grate or grid for such a gasifier which is self-cooling in operation. The invention additionally relates to an ash removal system for a gasifier of the above type used in conjunction with the air supply self-cooling grate or grid.
2. Description of the Prior Art
The gasification of wood and other solid fuels to produce a gaseous fuel is well known. Gasifiers for this purpose involve an endothermic reaction of steam with a burning fuel in a reactor vessel which is also supplied with a controlled amount of air. Wood gasifiers can be of the fluidized bed or fixed bed types and can operate continuously or cyclically.
In the known prior art, wood gasifiers typically involve a grate structure for the support or partial support of the fuel bed near and above the floor of the reactor vessel of the gasifier. There may be a void forming an ash plenum below the grate structure in the prior art gasifier. The grate may be in the form of a pinhole grate through which combustion air may enter the reactor vessel. Pinhole grates consisting of closely spaced grate tubes or members are satisfactory for fluidized bed gasifiers but are unsatisfactory for fixed bed gasifiers because they block or impede the downward movement of ash toward the floor of the reactor vessel, frequently causing clogging and slagging of the grate as well as grate burn-out. Some pinhole grates require internal passages for water coolant to avoid burnout. Moreover, the ash removal systems utilized in the prior art solid fuel gasifiers have tended to produce slag or clinker and have required relatively complex air locks or seals to prevent the air in the reactor vessel from escaping with the ash.